The present invention relates to a cylinder throw-on and throw-off mechanism for pressing/separating a blanket cylinder against/from printing cylinders such as a blanket cylinder and an impression cylinder and adjusting gaps with respect to the printing cylinders in various types of printing presses including an offset rotary press and an intaglio printing press.
A cylinder throw-on and throw-off mechanism of this type is disclosed in Japanese Utility Model Laid-Open No. 56-26249. In the cylinder throw-on and throw-off mechanism disclosed in this prior art, an eccentric bearing is pivoted using a motor as a driving source, thereby performing an impression-on/impression throw-off operation of a blanket cylinder axially supported by the eccentric bearing with respect to a plate cylinder and an impression cylinder. With this arrangement, the impression-on/impression throw-off operation is performed by driving a single eccentric bearing, resulting in a simple arrangement and a decrease in number of components.
In the above-described conventional cylinder throw-on and throw-off mechanism, however, a sheet thickness adjustment mechanism for adjusting a gap between the blanket cylinder and the impression cylinder in correspondence with the thickness of a paper sheet is not incorporated in the motor driving system. Instead, another eccentric bearing is manually pivoted. With this arrangement, the impression-on/impression throw-off operation cannot be performed in a manner interlocked with sheet thickness adjustment, and the sheet thickness adjustment operation is individually performed. Therefore, sheet thickness adjustment is troublesome and requires a long time, resulting in a complex arrangement.
Additionally, in the impression-on/impression throw-off operation, the phase and timing for pressing/separating the blanket cylinder against/from the impression or plate cylinder must be out of the printing range of both the cylinders, i.e., within a range where the gaps of the blanket cylinder and the impression or plate cylinder oppose each other, so as not to adversely affect the thickness of an ink coated on a plate. In the above-described conventional mechanism, since the impression-on/impression throw-off operation is not preformed while taking the phase between the cylinders into consideration, it is difficult to set the timing for the impression-of/impression throw-off operation. When the impression-on/impression throw-off operation is performed at an inappropriate timing, waste sheets are produced.